Cool Stars 14 - Submitted Abstract # 229
This version created on 05 October 2006

Disks Around Brown Dwarfs in the Ejection Scenario


Stefan Umbreit, Northwestern University
Hubert Klahr, Max-Planck-Institute for Astronomie Heidelberg
Thomas Henning, Max-Planck-Institute for Astronomie Heidelberg
Rainer Spurzem, Astronomisches Rechen-Institut Heidelberg
Seppo Mikkola, Turku University, Piikio, Finnland

We investigate the properties and frequencies of disks around brown
dwarfs formed in the ejection scenario for various young star-forming
regions.  For this, disk collision simulations in close triple
approaches are carried out and the post-encounter radial surface
density profile is characterized in dependence of the minimum
encounter distances between the escaper and the perturbers.  The
resulting post-encounter disk model is then applied to disks around
escaping brown dwarfs from decaying accreting triple systems, which
may also produce the close brown dwarf binaries observed in the
galactic field.  We find that the disks have very small sizes just
after the encounter, in our sample mostly less than 2 AU.  This is the
result of the very close two-body encounters taking place in accreting
non-hierarchical triple systems.  After we evolve these disks
viscously to match the typical ages of observed brown dwarfs we find
that they are no longer compact and it becomes increasingly difficult
to distinguish them from typical disks around TTauri stars based on
their size alone.  Furthermore, we find that the disks around the
ejected brown dwarfs have life-times that are mostly compatible with
accretor disk fractions derived from recent surveys for different
star-forming regions.  We conclude that very close collisions required
to eject brown dwarfs from unstable triple systems may not necessarily
lead to lower life-times and smaller disk sizes compared to TTauri
stars.

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